http://youtu.be/MhavOq8O0Ho Lung cancer is a disease where cells in the lungs multiply uncontrollably. The extra cells take up space in the lungs and impair gas exchange and the lung's ability to expel dirt. Learn how smoking, radon gas, and air pollution increase the risk of lung cancer. More free lessons at: http://www.khanacademy.org/video?v=MhavOq8O0Ho Practice questions related to these concepts here: https://www.khanacademy.org/test-prep/NCLEX-RN/rn-respiratory-system-diseases/rn-lung-cancer/e/lung-cancer-quiz Find more free videos, practice questions, and articles related to health and medicine, at: https://www.khanacademy.org/science/health-and-medicine Subscribe to Khan Academy Medicine at: http://youtube.com/subscription_center?add_user=khanacademymedicine These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.